"When the shark bites, with his teeth dear....."

Very clever idea and may be more practical to use on a land animal than a shark. You know, the lion that's gnawing on your arm kind of scenario. I am sceptical of the ability to actually plunge a long knive blade into a shark and then have time to hit the compressor button. My experience with sharks is that they move pretty darn fast, especially when tickled.

But I do have a technical question: wouldn't the air shooting out act like a propellant and the knife become a rocket, going the other way?